Piston



Dec. 30, 1941. E. G. FAHLMAN PISTON Filed March 10, 194.

I INVENTOR Everett G. Fahlman ATTORNEYS Patented Dec. 30, 1941 PISTON Everett G. Fahlman, Lakewood, Ohio, assignor to The Pei-mold Company, Cleveland, Ohio, a corporation of Ohio Application March 10, 1941, Serial No. 382,523

13 Claims.

This invention relatesto pistons such as are used for internal combustion engines, and more particularly to such pistons made of aluminum or alloys thereof.

In the usual construction of aluminum or aluminum alloy pistons for use in connection with cylinders of cast iron or other similar metals having a coefficient of expansion less than that of aluminum and its alloys, considerable diiliculty has been experienced in fitting the pistons so as to provide eflicient operation in the engine. One of the chief difliculties relates to the-clearance between the piston and the cylinder wall. If the clearance is properly adjusted for low temperatures, the difference in thermal expansion will cause the pistons to have insufficient clearance when operated at elevated temperatures, thus causing a possible injury to the cylinder walls of the engine. On the other hand, if the clearance is adjusted so that the engine will run properly at high temperatures, the clearance at low or starting temperatures will be excessive.

It is, therefore, an object of the present invention to provide an aluminum or aluminum alloy piston for use in an internal combustion engine or the like, which may be fitted to the cylinder,

and which will maintain an efficient clearance at normal operating temperatures.

Another object is to provide such a piston which will efliciently conduct the heat absorbed by the head portion to the cylinder walls, thereby avoiding an undesirable elevation of temperature in the skirt of the piston.

A further object is to provide a piston of this character in which the aluminum or aluminum alloy head portion is peripherally separated from the skirt portion, but is operatively connected thereto by means of a metallic yoke in such a manner that a minimum proportion of the heat absorbed by the head portion is transferred to the skirt portion, and in which the operating forces of the engine are transferred directly from the head portion to the wrist pin bosses in the skirt portion.

A still further object is to provide-a piston of this character which is simple in construction, inexpensive to manufacture, and which may be readily modified to adapt it for use in different types of internal combustion engines.

Other objects and advantages will appear from a study of the following detailed description made in connection with the accompanying drawing, in which Figure 1 is a side elevation of a piston embodying the present invention.

Fig. 2 is a section on the line 2-4 of Fig. 1.

Fig. 3 is atop view of the piston illustrated in Fig. 1.

Fig. 4 i a section on the line 44 of Fig. 1.

Fig. 5 is fragmentary section on the line 5-5 of Fig. 3.

Fig. 6 is a view in perspective of the metallic yoke used in joining the head portion to the skirt portion of the piston of the present invention.

The head portion I of a piston embodying the present invention comprises the compression or end wall 2 and an annular packing ring flange or side wall 3 which is formed with a suitable number of packing ring grooves l.

An inverted yoke, preferably U-shaped in section, connects the head and skirt of the piston. It is preferably formed of a metal, such as iron or steel, substantially stronger than the metal of which the head is made. Such a metal will usually be stronger than the metal of the skirt, although it is contemplated to construct pistons embodying the present invention having yoke and skirt formed integrally of a single kind of metal.

As best seen in Fig. 6, the yoke is preferably channel-shaped in section, having a body portion 1 and depending flange portions 8. The curvature of the body portion 1 is such that it seats snugly against and has the same contour as the internal surface of the end wall 2 andpacking ring flange 3 of the head portion of the piston. The yoke is provided with bifurcated ends formed by extensions of the flanges 8, each flange extension being arcuately shaped to form an anchor 9. It is preferable to secure the ends ID of -the anchors 9, such as by welding, in order to strengthen the yoke structure. Furthermore, the curvature of the anchors 9 is such that they may be embedded in the metal of the wrist pin bosses, so that the bearing surface for the wrist pin may be entirely of the metal of the wrist pin boss.

The yoke is rigidly secured in any suitable manner to a relatively small area of the central portion of the head I, such as by a suitable mechanical interlock. As shown, the body portion 1 of the yoke is centrally provided with apertures l2, and the adjacent portions of the flanges 8 are also provided with longitudinal slots 13, so that in forming the piston the meted out of which the head portion is formed may flow through and fill the apertures l2 and slots l3 and envelop part of the body portion I to form a holding boss ll depending from the central portion of the end wall 2 to secure the yoke to the head portion of the piston. It is to be noted that the holding boss II includes a relatively small area of the head I of the piston, and the metal of which the head and holding boss are formed does not entirely surround the yoke; so that expansion of the head has a minimum effect on the yoke.

This feature of construction is particularly advantageous when forming the head of the piston of a metal having a different thermal expansion than that of which the yoke is made. If, for instance, the yoke is a steel stamping and the head of the piston is cast of an aluminum alloy which has a greater thermal expansion than the steel, the yoke is firmly secured to the head under all normal temperatures. Assuming a tem- ,perature at which there is no stress between the yoke and the metal securing the yoke to the head of the piston, if the temperature should fall, the metal forming the holding boss I4, having a greater thermal expansion than the steel of the yoke, would tend to contract, thereby firmly grip-' ping the yoke. On the other hand, if the temperature should rise, the metal of the holding boss I4 within the apertures I2 and slots I3 would tend to expand more than the surrounding metal of the yoke, consequently securely holding the yoke and head portion together.

To those skilled in the art, it will be apparent that the piston of the character herein described may be readily cast in a permanent mold without the use of sand cores. The yoke B may be positioned upon and supported in place in the mold cavity by permanent core members, so that when the molten metal is introduced into the casting cavity it may flow around and enclose the anchors 9 and form the holding boss I4, yet leave the intermediate portion I5 of the yoke between the anchors and the holding boss I4 positioned against the internal surface of the head of the piston, but not secured thereto.

In such casting operation the head I and skirt I6 may be cast integrally, with the yoke 6 in position as mentioned above. After removal from the mold, a circumferential slot I1 is machined in the cast metal just above the wrist pin bosses IlB, thus defining the head I and skirt I6; If desirable, the packing ring grooves 4 may also be formed by a machining operation.

It will be seen that the present invention provides a piston having a head portion peripherally separated from the skirt and connected thereto only by a yoke having a relatively small crosssectional area, and which may be of a metal having relatively low thermal conductivity, so that a relatively small proportion of ,heat will be conducted from the head of the piston to the skirt thereof. It is to be noted that the piston is provided with a yoke which transmits the operative forces of an internal combustion engine directly from the head of the piston to the wrist pin bosses, so that substantially none of such forces are carried by the skirt of the piston. The yoke has its extremities attached securely to the wrist pin bosses by the anchors 9, which are embedded therein, thus providing a strong and rigid construction which minimizes the possibility of the yoke being pulled out of the wrist pin bosses during operation of the piston. Although a central portion of the yoke is partially embedded in the holding boss which forms a relatively small proportion of the metal of the head of the piston, it is seen that the portion of the yoke so embedded does not include the entire cross-section of the yoke. Thus, the yoke extends from one wrist pin boss to the other without having any intermediate-cross section completely embedded in the metal of the head of the piston.

By providing a yoke of the character described for use in connection with the pistons having a separated head and skirt portions, 2. very efficient and serviceable piston may be made. .Since the yoke is anchored to the head onlyv at the central portion by means of the holding boss I4, expansion of the head I may take place without being transmitted to the skirt I6, and without subjecting the skirt of the yoke 6 to stress, since the side wall 3 may expand away from the yoke 6. However, on a firing or compression stroke of an engine, when considerable force is exerted on the head of the piston, and must be transmitted to the wrist pin of the connecting rod, such force may be readily sustained by the yoke herein described, since it is afforded substantial lateral support by the internal surface of the head I. This is because the yoke is formed to fit against the internal contour of the surface of the head portions, so that the only unsupported part of the yoke is that adjacent the circumferential slot II.

It is to be understood, however, that the particular form of structure shown and described and the particular procedureset forth are presented for purposes of explanation and illustration, and that various modifications thereof are contemplated without departing from my invention as defined in the appended claims.

What I claim is:

1. A hollow piston comprising a head portion, a cylindrical skirt portion having wrist pin bosses and peripherally separated from the head portion by a circumferential slot, and a yoke of different metal than the head connecting the head and skirt, said yoke having end portions secured to the wrist pin bosses and a central portion embedded in a relatively small central portion of the head whereby expansion of the head has a minimum effect on the yoke.

2. A hollow piston comprising a head portion, a cylindrical skirt portion having wrist pin bosses and peripherally separated from the head portion by a circumferential slot, and a yoke of dif ferent metal than the head connecting the head and skirt, said yoke having end portions secured to the wrist pin bosses and a central portion embedded in a holding boss, said holding boss depending from the central part of the head of the piston and forming a relatively small portion thereof, whereby expansion of the head has a minimum effect on the yoke.

3. A hollow piston comprising a head portion, a cylindrical skirt portion having wrist pin bosses and peripherally separated from the head portion by a circumferential slot, and a yoke of different metal than the head connecting the head and skirt, said yoke having ends attached to the wrist pin bosses by anchors embedded therein and a center attached to the head by a portion embedded therein, said embedded portion being less than the total cross section of the yoke at that pointwhereby the yoke is uninterruptedly exposed from one wrist pin boss to the other.

4. A hollow piston comprising a head portion, a cylindrical skirt portion having wrist pin bosses and peripherally separated from the head portion by a circumferential slot, and a yoke of different metal than the head connecting the head and skirt, said yoke having a central portion secured to the head, end portions secured to the wrist pin bosses, and portions intermediate said central portion and the circumferential slot formed to correspond to the contour of the inner surface of the head.

5. A hollow piston comprising a head portion, a cylindrical skirt portion having wrist pin bosses,

and peripherally separated from the head portion.

by a circumferential slot, and a yoke of different metal than the head connecting the head and skirt, said yoke having a central portion secured to the head, end portions secured to the wrist pin bosses, and portions intermediate said central portion and the circumferential slot formed to correspond to the contour of the inner surface of the head, said intermediate portions engageable with the head of the piston.

6. A hollow piston comprising a head portion, a cylindrical skirt portion having wrist pin bosses, and peripherally separated from the head portion by a circumferential slot, and a yoke of different metal than the head connecting the head and skirt, said yoke having a central portion secured to the head, end portions secured to the wrist pin bosses, and portions intermediate said central portion and the circumferential slot formed to correspond to the contour of the inner surface of the head, said intermediate portions in contact with, and separable from the head portion of the piston upon thermal expansion thereof.

7. A hollow piston comprising a head portion, a cylindrical skirt portion having wrist pin bosses and peripherally separated from the head portion by a circumferential slot, and a yoke of different metal than the head connecting the head and skirt, said yoke having a central portion secured to the head, end portions secured to the wrist-pin bosses, said end portions encircling and embedded in the metal of the wrist pin bosses for securely anchoring the yoke thereto, and portions intermediate said central portion and the circumferential slot formed to correspond to the contour of the inner surface of the head.

8. A hollow piston comprising a head portion, a cylindrical skirt portion having wrist pin bosses and peripherally separated from the head por tion by a circumferential slot, and a yoke of different metal than the head connecting the head and skirt, said yoke having a central portion secured to the head, end portions secured to the wrist pin bosses, said end portions encircling and embedded in the metal of the wrist pin bosses for securely anchoring the yoke thereto, the openings in said end portions being larger in diameter than the wrist pin hole whereby the bearing surface defining said wrist pin hole is entirely of the metal of the wrist pin boss.

9. A hollow piston comprising a head portion, a cylindrical skirt portion having wrist pin bosses and peripherally separated from the head por tion by a circumferential slot, and a yoke of different metal than the head connecting the head and skirt, said yokehaving a central portion secured to the head by means of a holding boss formed integrally with the head of the piston, end portions secured to the wrist pin bosses, and portions intermediate said central portion and the circumferential slot formed to correspond to the contour of the inner surface of the head.

10. A hollow piston comprising a head portion, a cylindrical skirt portion having wrist pin bosses and peripherally separated from the head portion by a circumferential slot, and a yoke of different metal than the head connecting the head and skirt, said yoke having a central portion secured to the head by mean of a holding boss formed integrally with the head of the piston, said boss encircling a portion of the yoke, end portions secured to the wrist pin bosses, and portions intermediate said central portion and the circumferential slot formed to correspond to the contour of the inner surface of the head.

11. A hollow piston comprising a head portion, a cylindrical skirt portion having wrist pin bosses and peripherally separated from the head portion by a circumferential slot, and a yoke of different metal than the head connecting the.

head and skirt, said yoke having a central portion secured to the head by means of a holding boss formed integrally with the head of the piston, said boss encircling a portion of the yoke, and having integral portions extending through apertures in the yoke, end portions secured to the wrist pin bosses, and portions intermediate said central portion and the circumferential slot formed tocorrespond to the contour of the inner surface of the head.

12. A hollow piston comprising a head portion, a cylindrical skirt portion having wrist pin bosses and peripherally separated from th head portion by a circumferential slot, and a channel shaped yoke of different metal than the head connecting the head and skirt, said yoke having a central portion secured to the head and the web of the channel positioned against the inner surface of the head, and arcuately shaped anchors formed integrally with the flanges of the channel embedded in the metal of the Wrist pin bosses and encircling wrist pin receiving holes in EVERETT G. FAHLMAN. 

